A wide range of digital communications systems can be used for the transport of compressed digital video signals including the Motion Picture Experts Group (MPEG) format signals. Digital video will be a standard for the transmission of television signals, and eventually the majority of television signals will be transported in a digital format.
Asynchronous Transfer Mode (ATM) networks, which are used to transport information using statistical multiplexing, can be used to transport MPEG signals which are placed in ATM cells and routed through ATM networks. Cell loss, cell misrouting, and the corruption of information in cells caused by bit errors which occur during transmission can all lead to the corruption of MPEG digital video information.
Because the efficiency of ATM networks relies in part on the ability of the services to deal with occasional cell loss, and because ATM networks have no retransmission protocol, cell loss and the corruption of packets of MPEG information are inevitable.
Loss of MPEG information can result in significant degradation of the image quality, and can result in image "freezing" or "blocking." Such problems have not occurred in traditional analog television systems because occasional noise resulted in "snowy" images, which if infrequent, were not perceived by the viewer. MPEG video decoders, which decompress the video signal and produce final images for viewing, can handle some MPEG packet loss and corruption without significant degradation in the final picture, but the ability of the MPEG decoder to handle corrupted data depends in part on identifying which MPEG packets have been lost or corrupted.
For the foregoing reasons, there is a need for a method and apparatus for handling errors in a digital video transport system.